Time Machine and File Corruption Problem

Time Machine and File Corruption Problem

I have a file, and I'll just call it TGR.mov. I had this file in the same folder on the same drive (the internal drive) for months.

One day (mid-November, 2023) I found it was corrupted! It is a video, and it freezes at about 2:00 for two seconds with two artifacts, and then the video was fine, but with two seconds of loud static. It's always the same corruption on all corrupted copies. (I made many restores from different TM backups, and from Backblaze and OneDrive.)

I have backups going in parallel to two hard drives. 

On one drive, the file in the backup for 2023-08-22 is fine, but the same file in the very next backup, 2023-08-29, is corrupted.

On the other drive, the file never got corrupted. It's the same backup process backing up the same file in the same folder, only alternating between TM disks. 

What might have caused this? Any ideas? As best as I can recall, I never modified or moved the file from well before to well after those dates. Maybe the 2023-08-29 backup was interrupted, possibly by a reboot? Just a guess.

I've had other related files (specifically, two fcpbundle files) corrupted, but it is harder to track down what happened, as the Modified Date field is updated to the current time every time you view the fcp library. Only the created date remains the same. It is also much easier to open a .mov file than to open the file in Final Cut, click a few necessary things to get the right clip up, and then view the clip.

By the time stamps of the original file, TGR.mov, and the zip and tar files of this file, I can get some clues. 

By examining the milliseconds field, I can tell if the file is an original, was extracted from a zip file, or extracted from a tar file: If the Modified and Created Times are different, it's an original. If the times are the same, it's from a tar file. If the times are the same, but the milliseconds field is 000, it's from a zip file. I did not explore yet what happens to the times on files recovered from Backblaze and OneDrive, but they each gave an uncorrupted copy of TGR.mov. 

I did many restores from different folders and such trying to figure out what happened. I did notice that I restored the file from OneDrive around 2023-07-19, and they are all fine. Then around 2023-08-06 I made a tar file. It contains a corrupted copy of TGR.mov.

So if it was the original file that got corrupted -- and I find this more likely than not -- the corruption happened sometime between 2023-02-19 and 2023-08-06. But what, exactly, happened?

CHRONOLOGY:

2023-02-06 (near and around 2023-02-06) I was working on my old Mac to make an export from Final Cut, which became this file, documented in the chronology below. I needed the old Mac because the noise reduction plugin (for Final Cut) doesn't work on my new machine, and I used "sneaker-net" to move the files between the two Macs. I later had big problems with the drive I shuttled back and forth via sneaker-net. So maybe that drive is to blame. But still, why did only one of the running-in-parallel TM backups get corrupted? And if was the sneaker-net drive, then where did the good copy of TGR.mov come from?

2023-02-06 16:17:43.697 Created the original TGR.mov file

2023-02-06 16:18:03.238 Modification date of the original TGR.mov file

2023-02-19 Made a zip file of it. The TGR.mov file is okay.

2023-07-20 Restored a copy from OneDrive. Zip appears to have been involved based on the M. and C. dates. Or it could be a OneDrive thing. The TGR.mov file is okay.

2023-08-06 Made a tar file of it. The TGR.mov file in this tar file is corrupted.

2023-08-22 Backups of the TGR.mov file on drive 1 up to and incl. this date are fine.

2023-08-29 Backups of the TGR.mov file on drive 1 after and including this date are corrupted.

All dates: Backups of the TGR.mov file on drive 2 are all fine. No file corruption.

Unfortunately, there are almost certainly some actions or details I missed. But if you can give any hints or possibilities as to what happened, I would be very grateful.

If you need some specific details not given above, please do ask, and I'll try to get them for you.

Thanks!